PARP Inhibitors: A Proven Class Facing Limits

Why It Matters

Accurate patient selection and next‑generation PARP strategies are critical to sustain the therapeutic and commercial momentum of DNA‑repair‑targeted oncology.

Key Takeaways

• BRCA-mutant tumors show strongest, most consistent PARP inhibitor benefit
• HRD testing lacks predictive power, limiting broader PARP use
• Resistance via BRCA reversion and replication adaptation reduces efficacy
• New selective PARP1 inhibitor saruparib enters phase‑3 trials
• Combination strategies target ATR or Polθ to overcome resistance

Pulse Analysis

The rise of PARP inhibitors marked a paradigm shift in precision oncology, turning a molecular weakness—defective homologous recombination—into a druggable target. By trapping DNA lesions that cancer cells cannot repair, agents such as olaparib and niraparib quickly secured approvals across ovarian, breast, pancreatic, and prostate cancers, generating multi‑billion‑dollar revenues and prompting a wave of companion diagnostics. This success story underscores how mechanistic insight can accelerate market entry when a clear biomarker, like BRCA mutation, aligns with clinical benefit.

However, the enthusiasm has been tempered by practical challenges. HRD assays, while expanding eligibility, suffer from low negative predictive value and rely on historical genomic scars rather than real‑time repair capacity, leading regulators to narrow indications—as seen with the recent FDA restriction of Zejula to HRD‑positive ovarian tumors. Simultaneously, tumors develop resistance through BRCA reversion mutations or adaptive replication stress pathways, eroding response durability. Hematologic toxicities, especially anemia and thrombocytopenia, also demand dose modifications, complicating combination regimens with androgen‑receptor inhibitors or chemotherapy.

Looking forward, the industry is betting on refined pharmacology and smarter combos to revitalize the class. AstraZeneca’s saruparib (AZD5305) selectively blocks PARP1, aiming to reduce myelosuppression and improve synergy with other agents. Parallel efforts target complementary DNA‑damage‑response nodes—ATR inhibitors like ceralasertib and Polθ inhibitors such as ART6043—to bypass resistance mechanisms and broaden the therapeutic window. Success will hinge on developing robust, dynamic biomarkers that predict who will benefit and for how long, positioning next‑generation PARP strategies as a cornerstone of integrated cancer care.